This invention relates to a cutting head for a selective cutting machine.
Typically, such a cutting head is mounted on a boom, and is provided with a high pressure water supply line arranged on the boom. The supply line is connected, by means of a high pressure water duct, to a sliding member which is loaded by the pressurised water and is adjustable against a control surface of the rotating cutting head. The sliding member is formed with a duct which connects the high pressure water duct to the control surface; and control ducts, which open onto the control surface, are provided. The control ducts are arranged on a common graduated circle, and lead to the spray nozzles of the cutting head.
Selective cutting machines are used to advance tunnels, galleries or the like, through faces and seams in underground mines and for the winning of mineral deposits. Such a machine is equipped with a cross-axis cutting assembly having two cutting heads mounted on a pivotal boom, the two cutting being driven by a shaft orientated transversely to the boom (Journal "Gluckauf", 1985, page 1206). To abate the dust formed during cutting operations, to assist the cutting work by cooling the cutting tools, and to avoid methane flame scarfing in fire-damp mines, it is necessary to spary the working region with water under pressure. Generally, internal spraying is adopted, that is to say water under pressure is supplied from the exterior, and is introduced into the cutting heads via rotary arrangements. The pressurized water is then conveyed, via high pressure water ducts in the cutting heads, to spray nozzles arranged on the periphery of the cutting heads. A cutting head having such internally-fed spray nozzles is usually equipped with means for controlling the supply of pressurized water which ensures that water is fed only to the spray nozzles located in the region of the cutting head whose cutting tools are actually cutting (see DE-OS No. 28 10 982 and EP-PS No. 10 534).
In many applications, it is necessary to spray water intentionally into the working region of the individual cutters, that is to say into the cutting tracks thereof, in such a way that effective cooling of the cutting zones is achieved, whilst ignition of issuing methane gases by spark formation in the cutting zone is prevented. Operating pressures of the order of at least 100 to 200 bar, and often even of 300 bar and higher. are required for the spray water. Considerable sealing problems arise at such high working pressures if the rotary arrangement is arranged on the drive shaft or hub of the cutting head. The sealing problems are greater, the greater the diameter of the shaft or hub of the cutting head provided with the rotary arrangement. When using a planetary gear positioned within a cutting head, the shaft diameter to be sealed by the rotary arrangement is not excessively large, so that the sealing problems can generally be solved, at least if the working pressures of the spray water are not too high. The conditions may be different if a mitre gear is provided instead of the planetary gear. The use of a mitre gear has the significant advantage over a planetary gear that a cutting head can have a reduced diameter. On the other hand, considerable problems arise in providing the resultant large diameter drive shaft with a rotary arrangement for the supply of pressurized water which acts as a reliable seal over a prolonged operating period at the high pressures required.
A further known cutting head has an internally-fed spraying arrangement in which a piston-like pressure ring surrounding the shaft acts as the sliding member for conveying pressurised water into the rotating cutting head and for controlling the supply of pressurized water in such a way that only those spray nozzles in the cutting region are supplied with pressurised water. The pressure ring carries a control ring, and is charged with pressurised water in such a way that the control ring is pressed axially against a control surface which rotates with the cutting head, and in which there are located control ducts through which the individual spray nozzles are supplied with the pressurised water (see DE-OS No. 31 22 955). This spraying arrangement necessitates relatively high production costs, and can give rise to sealing problems, in particular at the above-mentioned high pressures of the water used.
The object of the invention is to provide a cutting head having internally-fed spray means which permits internal spraying to be achieved, even at very high water pressures of up to 300 bar or higher, without particular problems of sealing and wear arising in use.